Isotopic labeling of soil water is a broadly used tool for tracing the origin of water extracted by plants and compute root water uptake (RWU) profiles with multi-source mixing models. In this study we show how such method may misconstrue time series of xylem water isotopic composition as temporal dynamics of RWU by simulating data collected during a tall-fescue rhizotron experiment with an isotope-enabled physical soil-root model accounting for variability in root traits.

Plant root water uptake (RWU) has been documented for the past 5 decades from water stable isotopic analysis. In this paper, we review the different methods for reconstructing RWU profiles on the basis of isotopic information and confront them with each other during a series of virtual experiments. Finally, we call for a development of approaches coupling physically based RWU models with controlled condition experimental setups.

The mechanistic Couvreur root water uptake (RWU) model that is based on plant hydraulics and links root system properties to RWU, water stress, and crop development can evaluate the impact of certain crop properties on crop performance in different environments and soils, while the Feddes RWU approach does not possess such flexibility. This study also shows the importance of modelling root development and how it responds to water deficiency to predict the impact of water stress on crop growth.

In this study a nine year simulation of complete model output of a coupled atmosphere-land surface-subsurface model on the catchment scale is discussed. We used the Neckar catchment in SW-Germany as the basis of this simulation. Since the dataset includes the full model output it is not only possible to investigate model behaviour and interactions between the component models but also use it as a virtual truth for comparison of for example data assimilation experiments.

Precipitation moves through the soil to become stream water. The fraction of precipitation that becomes stream water after 3 months (Fyw) can be calculated with the stable isotopes of water. Previously, this was done for all the isotope data available, e.g., for several years. We used 1 year of data to calculate Fyw and moved this calculation time window over the time series. Results highlight that Fyw varies in time. Comparison studies of different regions should take this into account.

Isotopic labeling of soil water is a broadly used tool for tracing the origin of water extracted by plants and compute root water uptake (RWU) profiles with multi-source mixing models. In this study we show how such method may misconstrue time series of xylem water isotopic composition as temporal dynamics of RWU by simulating data collected during a tall-fescue rhizotron experiment with an isotope-enabled physical soil-root model accounting for variability in root traits.

This study describes a 2-month dataset of ground-based, vertically pointing triple-frequency cloud radar observations recorded during the winter season 2015/2016 in Jülich, Germany. Intensive quality control has been applied to the unique long-term dataset, which allows the multifrequency signatures of ice and snow particles to be statistically analyzed for the first time. The analysis includes, for example, aggregation and its dependence on cloud temperature, riming, and onset of melting.

To obtain magnitudes of flux components of H2O and CO2 (e.g., transpiration, soil respiration), we applied source partitioning approaches after Scanlon and Kustas (2010) and after Thomas et al. (2008) to high-frequency eddy covariance measurements of 12 study sites covering various ecosystems (croplands, grasslands, and forests) in different climatic regions. We analyzed the interrelations among turbulence, site characteristics, and the performance of both partitioning methods.

This paper presents and analyzes a global database of soil infiltration data, the SWIG database, for the first time. In total, 5023 infiltration curves were collected across all continents in the SWIG database. These data were either provided and quality checked by the scientists or they were digitized from published articles. We are convinced that the SWIG database will allow for a better parameterization of the infiltration process in land surface models and for testing infiltration models.

Focusing on the usage of integrated models and in situ Earth observatory networks, three challenges are identified to advance understanding of ESD, in particular to strengthen links between biotic and abiotic, and above- and below-ground processes. We propose developing a model platform for interdisciplinary usage, to formalize current network infrastructure based on complementarities and operational synergies, and to extend the reanalysis concept to the ecosystem and critical zone.

Different crop growths had consequences for the parameterization of root water uptake models. The root hydraulic parameters of the Couvreur model but not the water stress parameters of the Feddes–Jarvis model could be constrained by the field data measured from rhizotron facilities. The simulated differences in transpiration from the two soils and the different water treatments could be confirmed by sap flow measurements. The Couvreur model predicted the ratios of transpiration fluxes better.

Estimated values of selected key CLM4.5-BGC parameters obtained with the Markov chain Monte Carlo (MCMC) approach DREAM(zs) strongly altered catchment-scale NEE predictions in comparison to global default parameter values. The effect of perturbed meteorological input data on the uncertainty of the predicted carbon fluxes was notably higher for C3-grass and C3-crop than for coniferous and deciduous forest. A future distinction of different crop types including management is considered essential.

To maintain its yield, a plant needs to transpire water that it acquires from the soil. A deep understanding of the mechanisms that lead to water uptake location and intensity is required to correctly simulate the water transfer in the soil to the atmosphere. This work presents novel and general solutions of the water flow equation in roots with varying hydraulic properties that deeply affect the uptake pattern and the transpiration rate and can be used in ecohydrological models.

Applications of data assimilation (DA) arise in many fields of geosciences, perhaps most importantly in weather forecasting and hydrology. We want to investigate the roles of data assimilation methods and land surface models (LSMs) in joint estimation of states and parameters in the assimilation experiments. We find that all DA methods can improve prediction of states, and that differences between DA methods were limited but that the differences between LSMs were much larger.

Global climate models require adequate parameterization of soil hydraulic properties, but typical resampling to the model grid introduces uncertainties. Here we present a method to scale hydraulic parameters to individual model grids and provide a global data set that overcomes the problems. It preserves the information of sub-grid variability of the water retention curve by deriving local scaling parameters that enables modellers to perturb hydraulic parameters for model ensemble generation.

Soil moisture is a major variable that affects regional climate, weather and hydrologic processes on the Earth's surface. In this study, real-world data of a network of cosmic-ray sensors were assimilated into a regional land surface model to improve model states and soil hydraulic parameters. The results show the potential of these networks for improving model states and parameters. It is suggested to widen the number of observed variables and to increase the number of estimated parameters.

Plant root water uptake (RWU) has been documented for the past 5 decades from water stable isotopic analysis. In this paper, we review the different methods for reconstructing RWU profiles on the basis of isotopic information and confront them with each other during a series of virtual experiments. Finally, we call for a development of approaches coupling physically based RWU models with controlled condition experimental setups.

It is the first study to distinguish the species of nano-sized (d=1−20 nm), small-sized (d=20−450 nm) colloidal P, and dissolved P (d<1 nm) of hydromorphic surface grassland soils from Cambisol, Stagnic Cambisol to Stagnosol using FFF and 31P-NMR. Evidence of nano-sized associations of OC–Fe(Al)–PO43/pyrophosphate in Stagnosol. Stagnic properties affect P speciation and availability by releasing dissolved inorganic and ester-bound P forms as well as nano-sized organic matter–Fe/Al–P colloids.

In this work we show how we used a coupled atmosphere-land surface-subsurface model at highest possible resolution to create a testbed for data assimilation. The model was able to capture all important processes and interactions between the compartments as well as showing realistic statistical behavior. This proves that using a model as a virtual truth is possible and it will enable us to develop data assimilation methods where states and parameters are updated across compartment.

The Rollesbroich catchment is a hydrological observatory of the TERENO (Terrestrial Environmental Observatories) initiative. Hydrometeorological data and spatiotemporal variations in soil water content are measured at high temporal resolution and can be used for many purposes, e.g. validation of remote sensing retrievals, improving hydrological understanding, optimizing data assimilation and inverse modelling techniques. The data set is freely available online (http://www.tereno.net).

This paper describes the development of a modular data assimilation (DA) system for the integrated Earth system model TerrSysMP with the help of the PDAF data assimilation library.
Currently, pressure and soil moisture data can be used to update model states and parameters in the subsurface compartment of TerrSysMP.
Results from an idealized twin experiment show that the developed DA system provides a good parallel performance and is also applicable for high-resolution modelling problems.

Overall P content increased with decreasing size of soil aggregate-sized fractions. The relative distribution and speciation of varying P forms were independent of particle size. The majority of alkaline extractable P was in the amorphous Fe/Al oxide fraction, most of which was orthophosphate. Significant amounts of monoester P were also bound to these oxides. Residual P contained similar amounts of P occluded in amorphous and crystalline Fe oxides. This P may be released by FeO dissolution.

DasPy is a ready to use open source parallel multivariate land data assimilation framework with joint state and parameter estimation using Local Ensemble Transform Kalman Filter. The Community Land Model (4.5) was integrated as model operator. The Community Microwave Emission Modelling platform, COsmic-ray Soil Moisture Interaction Code and the Two-Source Formulation were integrated as observation operators for the multivariate assimilation of soil moisture and soil temperature, respectively.

This study introduces an extension of the classical two-tower approach for uncertainty estimation of measured net CO2 fluxes (NEE). Because land surface properties cannot be assumed identical at two eddy covariance towers, a correction for systematic flux differences is proposed to be added to the classical weather filter. With this extension, the overestimation of NEE uncertainty due to systematic flux differences (which are assumed to increase with tower distance) can considerably be reduced.

This paper presents the joint assimilation of cosmic-ray neutron counts and land surface temperature with parameter estimation of leaf area index at an irrigated corn field. The results show that the data assimilation can reduce the systematic input errors due to the lack of irrigation data. The estimations of soil moisture, evapotranspiration and leaf area index can be improved in the joint assimilation framework.

Interception is the storage and subsequent evaporation of rain by vegetation and surface litter. Quantifying interception is critical for understanding the water balance, but it can be difficult and costly to measure. We developed an approach to estimate interception using automated soil moisture measurements during rainfall events. Results suggest that interception can be estimated using soil moisture data, leading to potential cost savings and logistical advantages over conventional methods.

Fluorescent tracers such as uranine and sulforhodamine B are useful tools to gain knowledge about water and solute fluxes in aquatic and terrestrial ecosystems. In this study we systematically investigated the influence of important soil properties (pH, organic carbon content and texture) on tracer adsorption in soils and sediments. These properties also determine whether the tracers in the respective soil behave conservatively or non-conservatively.

Our field observation-based examination of flow path evolution, soil formation and vegetation succession across ten millennia shows how water flow paths and subsurface water storage are linked to the organization of evolving landscapes.
The found increase in water storage and preferential flow paths with increasing soil age shows the effect of the complex interaction of vegetation and soil development on flow paths, water balance, and runoff formation during landscape evolution.

Water flows through soils in an incredibly complex network of pathways. Understanding these pathways is critical to sustainable use of water resources. Ground-penetrating radar (GPR) can image water in near-surface soils the same way an X-ray is used to image the human body. Utilizing innovative ways of collecting and processing the GPR data, we can image complex water flow in space and through time, which allows for the continued development of our ideas and models of subsurface water flow.

In cold regions, the permeability of the frozen ground is an important factor influencing a watershed's response to snowmelt. This study highlights the effects of preferential flow in frozen soils on snowmelt redistribution and groundwater recharge in seasonally frozen landscapes.

This study presents an analysis of 135 soil moisture profiles for identification of the spatial and temporal preferential flow occurrence in a complex landscape. Especially dry conditions and high rainfall intensities were found to increase preferential flow occurrence in soils. This results in a seasonal pattern of preferential flow with a higher occurrence in summer. During this time grasslands showed increased flow velocities, whereas forest sites exhibited a higher amount of bypass flow.

Lack of adequate instrumentation for monitoring nutrient availability in agricultural soils leads in most cases to over-application of fertilizers, often resulting in groundwater pollution. This research presents a novel approach for real-time, in situ monitoring of nitrate in soils using absorption spectroscopy techniques while preventing interference from dissolved organic carbon. Column experiments with this system resulted in accurate nitrate measurements in three different soil types.

We carried out a series of laboratory-controlled experiments in order to simulate different scenarios of practical interest aiming to analyze, from a dielectric point of view, the influence of different washing solutions on non-aqueous phase liquid (NAPL) removal. Furthermore, on the basis of the results obtained, we validated a dielectric mixing model for predicting the volumetric amounts of NAPL (θNAPL) within the contaminated soil as the decontamination process progressed.

One of the main objectives of remote sensing methodology is to downscale soil moisture to improve irrigation management. The DISPATCH algorithm is able to measure soil moisture at 1 km resolution using SMOS and MODIS data. In this work DISPATCH has been evaluated with soil moisture sensors, under heterogeneous conditions where local irrigation is applied. Results show that DISPATCH is not sensitive when local irrigation is applied even at low resolution.

Gravity monitoring at the surface and in situ (in caves) has been conducted in a karst hydro-system in the south of France (Larzac plateau). Subsurface water storage is evidenced with a spatial variability probably associated with lithology differences and confirmed by MRS measurements. Gravity allows transient water storage to be estimated on the seasonal scale.

To extract water from soils for isotopic analysis, cryogenic water extraction is the most widely used removal technique. This work presents results from a worldwide laboratory intercomparison test of cryogenic extraction systems. Our results showed large differences in retrieved isotopic signatures among participating laboratories linked to interactions between soil type and properties, system setup, extraction efficiency, extraction system leaks, and each lab’s internal accuracy.

Understanding water infiltration in karst regions is crucial as the aquifers they host provide drinkable water for a quarter of the world's population. We present a non-invasive tool to image hydrological processes in karst systems. At our field site, the injection of electrical current in the ground, repeated daily over a 3-year period, allowed imaging changes in the groundwater content. We show that specific geological layers control seasonal to rainfall-triggered water infiltration dynamics.

The paper aims to infer the bulk electrical conductivity distribution in the root zone from EMI readings. TDR measurements were used as ground-truth data to evaluate the goodness of the estimations by EMI inversion. The approach is based on the mean and standard deviation of the EMI and TDR series. It looks for the physical reasons for the differences between EMI- and TDR-based electrical conductivity and provides a correction of the bias based on the statistical sources of the discrepancies.

Satellite and broad-scale model estimates of soil moisture have improved in resolution. However, validation and calibration of these products has been limited because of a lack of observations on corresponding scales. We use a mobile soil moisture monitoring platform, known as the rover, to derive soil moisture at 9 km and 1 km resolution. We describe methods to calculate soil moisture and present results from multiple surveys. The products produced are well suited to validation studies.

In this paper we present a case study from a heterogeneous pasture site in the Canadian prairies, where we have quantified the various components of the water balance on the field scale, and critically examine some of the simplifying assumptions which are often invoked when applying water budget approaches in applied hydrology. We highlight challenges caused by lateral fluxes of blowing snow and ambiguous partitioning of snow melt water into runoff and infiltration.

A field-scale average of near-surface water content can be sensed by cosmic-ray neutron detectors. To interpret, calibrate, and validate the integral signal, it is important to account for its sensitivity to heterogeneous patterns like dry or wet spots. We show how point samples contribute to the neutron signal based on their depth and distance from the detector. This approach robustly improves the sensor performance and data consistency, and even reveals otherwise hidden hydrological features.

This study uses a newly designed lysimeter to study three consecutive years (2013–2015) of deep soil recharge (DSR) underneath bare sand land on the eastern margin of Mu Us Sandy Land in the Ordos Basin of China. The objective is to identify the characteristics of the DSR distribution and the factors affecting the DSR distribution. Specifically, we would like to examine if the commonly used recharge coefficient concept can be applied for arid and semi-arid regions.

In situ bioremediation of a perchlorate-contaminated vadose zone was conducted through infiltration of electron-donor-enriched water. A vadose zone monitoring system (VMS) provided real-time tracking of the hydraulic and chemical conditions across the unsaturated zone. Variations in concentration profiles of perchlorate, chloride, DOC and bromide in the vadose zone pore water showed limited migration capacity of biologically consumable carbon and significant mobilization of perchlorate.

This paper presents a detailed description of the new Swiss soil moisture monitoring network SOMOMOUNT, which comprises six stations distributed along an elevation gradient ranging from 1205 to 3410 m. The liquid soil moisture (LSM) data collected during the first 3 years are discussed with regard to their soil type and climate dependency as well as their altitudinal distribution. The elevation dependency of the LSM was found to be non-linear with distinct dynamics at high and low elevation.

Retardation of migrating contaminant vapors in the subsurface may mitigate groundwater contamination or vapor intrusion into buildings. An experimental investigation was conducted to quantify the retardation of carbon disulfide (CS2) vapor in moist porous media based on the analysis of concentration breakthrough curves. Findings linked retardation to types of porous media and water saturation. Moreover, the first evidence of biodegradation of the CS2 vapor was found in the column experiments.

With a process-based interpretation of electromagnetic induction measurements, we discussed the potential and limitations of such a method for soil moisture mapping. Results will help clarify the complex and time-varying effect of stable soil properties and dynamic state variables on the physical parameters measured, with implications for future studies. We highlighted the importance of time-series data and the need for a multidisciplinary approach for proper interpretation.

We investigated the potential use of trace element and stable oxygen-isotope variations in cave drip water as palaeorainfall proxies in an Australian alpine karst site. Using 7 years of cave monitoring data, we constrained the hydrological processes impacting the drip-water composition and identified a robust ENSO–drip water hydrochemical relationship. These findings are fundamental for reconstructing past ENSO variability from speleothems (cave deposits) regionally and globally.

Here we present a strategy to use globally available datasets in the calibration function used to convert observed moderated neutron counts into volumetric soil water content. While local sampling protocols are well documented for fixed probes, the use of roving probes presents new calibration challenges. With over 200 fixed probes and 10 roving probes in use globally, we anticipate this paper will serve as a keystone for the growing cosmic-ray neutron probe and hydrologic community.

Efficient groundwater protection from pollution originating in agriculture requires effective monitoring means capable of tacking pollution processes in the vadose zone, long before groundwater pollution turns into an unavoidable fact. In this study, a vadose zone monitoring system that was installed under a crop field fertilized by dairy slurry enabled real-time tracking of nitrate plum migration down the vadose zone from the land surface to the water table at 18m depth.

The AWAT (Adaptive Window and Adaptive Threshold) filter routine for high-resolution lysimeter data is improved. The threshold scheme with original step interpolation yields unrealistic fluxes for high temporal resolution. Improvement applies linear and spline interpolation schemes so that fluxes in high temporal resolution are automatically calculated. The spline scheme allows continuous differentiability of filtered data so that any output resolution for the fluxes is sound.

Remote sensing techniques can provide useful large-scale estimates of soil moisture. However, these methods often only sense near-surface soil moisture, whereas many applications require estimates of the entire root zone. In this study we propose and test methods to "depth-scale" the shallow soil moisture measurements obtained using the cosmic-ray neutron probe to represent the entire root zone, thereby improving the applicability of this measurement approach.

It is usually assumed that soil properties are not affected by drought events. We used dye tracer experiments to test this assumption on six forest soils, which were forced into drought conditions. The results of this study show clear evidence for changes in infiltration pathways. In addition, most soils developed soil water repellency. Overall, the results suggest that the past climatic conditions are more important than the actual soil moisture status regarding hydrophobicity and infiltration.

Caves offer a natural inception point to observe both the long-term groundwater recharge and the preferential movement of water through the unsaturated zone of such limestone. In this study, we develop a method that combines automated drip rate logging systems and remote sensing techniques to quantify the infiltration processes within a cave.

The ensemble Kalman filter (EnKF) and simplified extended Kalman filter (SEKF) root-zone soil moisture analyses are compared when assimilating in situ surface observations. In the synthetic experiments, the EnKF performs best because it can stochastically capture the errors in the precipitation. The two methods perform similarly in the real experiments. During the summer period, both methods perform poorly as a result of nonlinearities in the land surface model.

Several methods for measuring unsaturated soil characteristics have been tested on sandy soil in northeastern Thailand, with different land uses. Each method shows significantly different parameters, regardless of land use. Nevertheless, when used for annual water balance modeling with HYDRUS1D, no noticeable differences for the various sets of parameters appeared. Any of these measurement method could be employed. Therefore, we recommended using the cheapest and easiest (i.e., Beerkan) method.

In this study, we analyze a set of high-resolution, surface-based, 2-D ground-penetrating radar (GPR) observations of artificially induced subsurface water dynamics. In particular, we place close scrutiny on the evolution of the capillary fringe in a highly dynamic regime with surface-based time-lapse GPR. We thoroughly explain all observed phenomena based on theoretical soil physical considerations and numerical simulations of both subsurface water flow and the expected GPR response.

Profiles of soil water stable isotopes were followed non-destructively and with high precision for a period of 290 days in the laboratory
Rewatering at the end of the experiment led to instantaneous resetting of the isotope profiles, which could be closely followed with the new method
The evaporation depth dynamics was determined from isotope gradients calculation
Uncertainty associated with the determination of isotope kinetic fractionation where highlighted from inverse modeling.

Profiles of soil water stable isotopes were followed non-destructively and with high precision...